Cell culture has generated considerable interest in recent years due to the revolution in genetic engineering and biotechnology. Cells are cultured to make for example proteins, receptors, vaccines, and antibodies for therapy, research, and for diagnostics.
It has long been recognized that perfusion culture offers relatively good economics for cell cultures. In this operation, cells are retained in the bioreactor, and the product is continuously removed along with toxic metabolic byproducts. Feed, containing nutrients, is added continually to the bioreactor. Perfusion culture operation is capable of achieving high cell densities and more importantly, the cells can be maintained in a highly productive state for weeks. This achieves much higher yields and reduces the size of the bioreactor necessary. It is also a useful technique for cultivating primary or other slow growing cells.
Perfusion operations have been greatly developed during recent years. U.S. Pat. No. 6,544,788 discloses a prior art bioreactor comprising a perfusion filter which allows liquid to be removed from the bioreactor without losing cells. The perfusion filter is constructed such that it is neutrally buoyant with respect to the culture media. It is placed inside the bioreactor so that it can move freely with bioreactor's rocking motion. The bottom surface of the filter consists of a liquid permeable, but cell-retentive membrane. A flexible tube allows the essentially cell-free filtrate to be drawn out from inside the filter. As the bioreactor is rocked, the filter moves rapidly back and forth in the culture media. This back and forth motion serves to clean the filter and allows it to operate without severe clogging. Nutrient feed is pumped into the bioreactor and the harvest filtrate is removed continuously, or at periodic intervals.
Even though the above-defined perfusion filter provides a satisfactory prevention of clogging of the filter, there is still a further desire to improve the prevention of clogging of the perfusion filter and extend the operational durability of the perfusion filter.
Documents U.S. Pat. No. 5,032,524, WO2007076865 and FR2679248 deal with the problems of clogging in filters in bioreactors. In each of the documents, a system including recirculation of liquid media is suggested. However, such systems are difficult to implement in bioreactors in which filter assembly is free to move within the chamber.